<i>η</i>pairing and off-diagonal long-range order in a Hubbard model

It is shown in a simple Hubbard model that through a mechanism called \ensuremath{\eta} pairing one can construct many eigenstates of the Hamiltonian possessing off-diagonal long-range order. The intrapair distance is small. It is shown that these eigenstates are metastable and possess an energy gap.